1. Field of the Invention
The present invention relates to a method of developing a photosensitive planographic printing plate which comprises a hydrophilic support and a photosensitive layer formed by applying to the hydrophilic support a positive photosensitive composition for an infrared laser and which has been exposed to an infrared light beam with an alkaline liquid developer containing at least one saccharide selected from non-reducing sugars and at least one base.
2. Description of the Related Art
Automatic developing machines for printing plates are being widely used in recent years in the plate-making and printing industries in order to rationalize and standardize plate-making operations. Such automatic developing machines generally comprise a development section and a post-treatment section, and include apparatus for conveying a printing plate, various processing liquid tanks and spray apparatus. After the printing plate has been exposed, the printing plate is developed using spray nozzles to spray the printing plate with the various processing liquids, which are pumped by a pump while the printing plate is conveyed horizontally. There is recently also known a method in which a printing plate is processed by immersing the printing plate in processing liquid tanks filled with processing liquids and conveying the printing plate therethrough with immersed guide rolls and the like. In such automatic processing, processing can be conducted while replenishing each processing liquid with replenishers in response to processing amount, operating time and the like.
A disposable processing method can also be applied, in which the printing plate is processed with substantially unused processing liquids.
Conventionally, when the image recording layer of the printing plate is developed, unnecessary portions of the recording layer are removed in the liquid developer liquid by brushing.
For example, when a thermal positive photosensitive planographic printing plate is used, the recording layer is irradiated with an infrared laser beam (light beam) on the basis of image data, whereby an infrared absorbent absorbs this light and generates heat. Thereafter, the plate is immersed in an alkali developer. Exposed portions are soluble in the alkali developer, and the recording layer containing the exposed portions is brushed with the brush roller to remove the exposed portions, whereby an image can be formed.
Channel brush rollers have conventionally been widely used as the brush roller, but they have a disadvantage in that brushing unevenness tends to occur. In order to prevent such brushing unevenness, it is necessary to increase the diameter of the roller.
There is also an apparatus in which a molten brush roller is used as a brush roller, instead of the channel brush roller. Because molten brush rollers are made of a material like fluffy cloth, they have advantages in that there is no rubbing unevenness and they are inexpensive in comparison with channel brush rollers.
However, molten brush rollers are not durable and must be replaced every 1 to 3 months under conditions of ordinary use. There are thus problems in that durability is 1/10-19 in comparison with channel brush rollers, and maintenance is poor.
In the case of a thermal positive photosensitive planographic printing plate, use of a molten brush roller makes it difficult to control pressure. The reason for this is that heat is predicted to transfer to an aluminum support because exposure is basically conducted using heat, and solubility with respect to a developer is set at a higher level.
However, when pressure is high at the time of brushing, it becomes easy for the recording layer itself to be scratched. Since controlling the pressure of a molten brush roller can only be done roughly, suitable pressure cannot be maintained.
Moreover, when a conventional silicate developer is used, deposits are easily formed. The deposit adheres to the brush roller and scratches the plate surface in some cases. Scratches resulting from such deposits become remarkable in the case of a thermal positive photosensitive planographic printing plate.